(a) Field of the Invention
The present invention pertains to a static induction transistor which exhibits an unsaturated drain current-drain voltage characteristic, and more particularly it pertains to an improvement of the SIT characteristic at low values of the drain current.
(b) Description of the Prior Art
The static induction transistor (SIT), which is a kind of majority carrier injection control device having an unsaturated drain current-drain voltage characteristic similar to the plate current-plate voltage characteristic of triode vacuum tubes, has been proposed in Japanese Patent application No. 46-28405 (the corresponding U.S. Patent application No. 817052) by Jun-ichi NISHIZAWA, one of the present inventors, and in Japanese Patent Application No. 46-57768 (the corresponding U.S. Patent application No. 576541) by Jun-ichi NISHIZAWA et al. The above-mentioned prior art SIT's are designed so that the product of the true transconductance and the series resistance of the SIT may be maintained lower than unity (one) at least in the operational range of low drain current irrespective of the magnitude of the gate voltage. Reference is also made to the Nishizawa U.S. Patent application Ser. No. 757,583 filed Dec. 27, 1976. Reference is also made to the Nishizawa U.S. Patent application Ser. No. 757,583, filed Dec. 27, 1976.
A typical gate voltage-drain current characteristic of the prior art SIT is plotted as the drain current I.sub.d versus the gate voltage V.sub.g, with the drain voltage V.sub.d serving as a parameter in a semi-log scale in FIG. 1. The drain currentdrain voltage characteristic is also plotted as I.sub.d versus V.sub.d, with V.sub.g serving as a parameter in a semi-log scale in FIG. 2. In FIG. 2, the dashed portion of characteristic curves is measured by pulse technique. These Figures show the fact that, in the high drain current region, the drain current is nearly proportional to the drain voltage as well as to the gate voltage, but that, in the lower drain current region below approximately 1.times.10.sup.-3 ampere for this specimen, both the drain current-drain voltage characteristic and the drain current-gate voltage characteristic are governed by an exponential rule. This non-linearity of the prior art SIT's at the low drain current region is considered to be responsible for the non-linear distortion by the SIT in various applications. Accordingly, it is desirable to eliminate the non-linearity in the SIT response.